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Key structure in laminar-turbulent transition of boundary layer with streaky structures

Theoretical & Applied Mechanics Letters 2019年第1期9卷 32-35,I0005页

作者： Joe Yoshikawa yu Nishio Seiichiro Izawa yu fukunishi Industrial Technology Institute Miyagi Prefectural Government Seikei University Tohoku University

A numerical simulation is performed to find out a key vortical structure in the laminar-turbulent transition. A low-speed streak is generated inside a laminar boundary layer using an isolated cuboid roughness, aimed at providing an environment unstable to outer disturbances. Then, a short duration jet is issued into the boundary layer. When the jet velocity is low, some vortices appear in the boundary layer, but the transition of the boundary layer does not take ***, when the jet velocity exceeds a certain threshold, two vortices newly appear above the elongated legs of a V-shaped vortex and only one of them is stretched and survives. After that,vortices are generated one after another around the survived one. By comparing the decayed and the survived vortices, it is found that the difference in their heights is the key characteristic which leads to the transition.

关键词： Turbulent onset Key vortical structure Laminar-turbulent transition Boundary layer Streaky structures Short duration jet Numerical simulation

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Numerical simulation of droplet-formation in rotary atomizer

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Theoretical & Applied Mechanics Letters 2019年第3期9卷 202-205页

作者： Naoki Igari Takuro Iso yu Nishio Seiichiro Izawa yu fukunishi Tohoku University

Numerical simulations of the liquid flow scattering from rotary atomizers are performed using an incompressible smoothed particle hydrodynamics (SPH) method. The influence of grooves at the edges of the atomizers on the formation of ligaments and droplets is investigated changing the numbers and shapes of the grooves. As a result, it is found that small droplets are likely to be generated when the number of grooves is large and the depth of grooves is deep. It is also found that the grooves work more effectively in bell-cup atomizers than in disk type atomizers.

关键词： Smoothed particle hydrodynamics (SPH) Rotary atomizer Grooves Droplet

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Morphology of Acetabulum and Femoral Head-Neck Junction in Hip Dysplasia Which Underwent Rotational Acetabular Osteotomy

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Open Journal of Orthopedics 2015年第5期5卷 126-134页

作者： Ryo Kanto Hiroshi Nakayama Shoji Nishio yuki Fujihara yu Takeda Shigeo fukunishi Shinichi Yoshiya Toshiya Tachibana Department of Orthopaedic Surgery Hyogo College of Medicine Nishinomiya Japan

The purpose of this study was to evaluate the preoperative radiographs with cases of developmental dysplasia of the hip (DDH) leading to rotational acetabular osteotomy (RAO) or curved peri-ace-tabular osteotomy (CPO), and examine the frequency of femoroacetabular impingement (FAI) related bone morphology in the acetabulum and femoral head-neck junction. Twenty-four hips with hip dyaplasia who underwent CPO or RAO were included in this study. Six hips had grade 0 and eighteen hips had grade 1 OA according to the Tönnis classification. We excluded patients with moderate and severe hip osteoarthritis and major femoral head deformities. Preoperative radiograph was evaluated on sharp angle, center-edge angle, alpha angle, crossover sign and posterior wall sign. Crossover signs were revealed in 7 hips (29.2%);posterior wall signs were revealed in 16 hips (66.7%);and cam-type deformities with an alpha angle of ≥50.5°were observed in 19 hips (79.2%) in preoperative evaluation. As determined using the Tönnis scale, no progression of osteoarthritis was found in 16 of the 24 hips;there was a one-grade progression in 8 hips. Among the 8 hips, either positive cross-over sign or posterior sign in acetabulum, and an alpha angle of ≥50.5°in femur were observed in six hips with progression of osteoarthritis. The presence of cam-type deformity and acetabular retroversion in patients who underwent RAO or CPO was relatively high in preoperative radiographs, and caution should be employed during surgery in patients with DDH. There is a possibility of secondary FAI due to excessive forward coverage of the bone fragments after RAO and CPO.

关键词： Acetabular Hip Dysplasia Acetabular Osteotomy Femoroacetabular Impingement

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